Innovation for Railway Bridge Decks: A Prebent Steel-VHPC Beam

An extensive experimental study has been carried out in the framework of the French National Project MIKTI devoted to innovative composite structures to extend the Belgian technique of composite prebent beams called “preflex” beams, to very high performance concrete (VHPC). By comparison with experience gained from the Belgian precast industry, the main advantage of using VHPC with silica fume is to reduce the prestressing losses of the system, thanks to a significant decrease of the creep in addition to the possibility of optimizing the weight and the span of the beam. Major issues of the research were to validate a design method at serviceability state related to concrete cracking and at ultimate limit state corresponding to instability of the steel girder and the preservation of the composite behaviour of the beam even after a large number of live load cycles. The analysis of the global response of two 13 m long beams monitored during several months allowed to conclude the feasibility to optimize a prebent beam with a VHPC.